Magnetic field plasma confinement for compact fusion power

ABSTRACT

In one embodiment, a fusion reactor includes two internal magnetic coils suspended within an enclosure, a center magnetic coil coaxial with the two internal magnetic coils and located proximate to a midpoint of the enclosure, a plurality of encapsulating magnetic coils coaxial with the internal magnetic coils, and two mirror magnetic coil coaxial with the internal magnetic coils. The encapsulating magnetic coils preserve the magnetohydrodynamic (MHD) stability of the fusion reactor by maintaining a magnetic wall that prevents plasma within the enclosure from expanding.

RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. § 119(e) of thepriority of the following U.S. Provisional Applications filed on Apr. 3,2013, the entire disclosures of which are hereby incorporated byreference: U.S. Provisional Application No. 61/808,136, entitled“MAGNETIC FIELD PLASMA CONFINEMENT FOR COMPACT FUSION POWER”; U.S.Provisional Application No. 61/808,122, entitled “MAGNETIC FIELD PLASMACONFINEMENT FOR COMPACT FUSION POWER”; U.S. Provisional Application No.61/808,131, entitled “ENCAPSULATION AS A METHOD TO ENHANCE MAGNETICFIELD PLASMA CONFINEMENT”; U.S. Provisional Application No. 61/807,932,entitled “SUPPORTS FOR STRUCTURES IMMERSED IN PLASMA”; U.S. ProvisionalApplication No. 61/808,110, entitled “RESONANT HEATING OF PLASMA WITHHELICON ANTENNAS”; U.S. Provisional Application No. 61/808,066, entitled“PLASMA HEATING WITH RADIO FREQUENCY WAVES”; U.S. ProvisionalApplication No. 61/808,093, entitled “PLASMA HEATING WITH NEUTRALBEAMS”; U.S. Provisional Application No. 61/808,089, entitled “ACTIVECOOLING OF STRUCTURES IMMERSED IN PLASMA”; U.S. Provisional ApplicationNo. 61/808,101, entitled “PLASMA HEATING VIA FIELD OSCILLATIONS”; andU.S. Provisional Application No. 61/808,154, entitled “DIRECT ENERGYCONVERSION OF FUSION PLASMA ENERGY VIA CYCLED ADIABATIC COMPRESSION ANDEXPANSION”.

TECHNICAL FIELD

This disclosure generally relates to fusion reactors and morespecifically to magnetic field plasma confinement for compact fusionpower.

BACKGROUND

Fusion power is power that is generated by a nuclear fusion process inwhich two or more atomic nuclei collide at very high speed and join toform a new type of atomic nucleus. A fusion reactor is a device thatproduces fusion power by confining and controlling plasma. Typicalfusion reactors are large, complex, and cannot be mounted on a vehicle.

SUMMARY OF PARTICULAR EMBODIMENTS

According to one embodiment, a fusion reactor includes two internalmagnetic coils suspended within an enclosure, a center magnetic coilcoaxial with the two internal magnetic coils and located proximate to amidpoint of the enclosure, a plurality of encapsulating magnetic coilscoaxial with the internal magnetic coils, and two mirror magnetic coilcoaxial with the internal magnetic coils. The encapsulating magneticcoils preserve the magnetohydrodynamic (MHD) stability of the fusionreactor by maintaining a magnetic wall that prevents plasma within theenclosure from expanding.

Technical advantages of certain embodiments may include providing acompact fusion reactor that is less complex and less expensive to buildthan typical fusion reactors. Some embodiments may provide a fusionreactor that is compact enough to be mounted on or in a vehicle such asa truck, aircraft, ship, train, spacecraft, or submarine. Someembodiments may provide a fusion reactor that may be utilized indesalination plants or electrical power plants. Other technicaladvantages will be readily apparent to one skilled in the art from thefollowing figures, descriptions, and claims. Moreover, while specificadvantages have been enumerated above, various embodiments may includeall, some, or none of the enumerated advantages.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates example applications for fusion reactors, accordingto certain embodiments.

FIG. 2 illustrates an example aircraft system utilizing fusion reactors,according to certain embodiments.

FIGS. 3A and 3B illustrate an example fusion reactor, according tocertain embodiments.

FIG. 4 illustrates a simplified view of the coils and example systemsfor energizing the coils of the fusion reactor of FIGS. 3A and 3B,according to certain embodiments.

FIG. 5 illustrates plasma within the fusion reactor of FIGS. 3A and 3B,according to certain embodiments.

FIG. 6 illustrates magnetic fields of the fusion reactor of FIGS. 3A and3B, according to certain embodiments.

FIG. 7 illustrates an internal coil of the fusion reactor of FIGS. 3Aand 3B, according to certain embodiments.

FIG. 8 illustrates a cut-away view of the enclosure of the fusionreactor of FIGS. 3A and 3B, according to certain embodiments.

FIG. 9 illustrates an example computer system, according to certainembodiments.

DESCRIPTION OF EXAMPLE EMBODIMENTS

Fusion reactors generate power by confining and controlling plasma thatis used in a nuclear fusion process. Typically, fusion reactors areextremely large and complex devices. Because of their prohibitivelylarge sizes, it is not feasible to mount typical fusion reactors onvehicles. As a result, the usefulness of typical fusion reactors islimited.

The teachings of the disclosure recognize that it is desirable toprovide a compact fusion reactor that is small enough to mount on or invehicles such as trucks, trains, aircraft, ships, submarines,spacecraft, and the like. For example, it may be desirable to providetruck-mounted compact fusion reactors that may provide a decentralizedpower system. As another example, it may be desirable to provide acompact fusion reactor for an aircraft that greatly expands the rangeand operating time of the aircraft. In addition, it may desirable toprovide a fusion reactor that may be utilized in power plants anddesalination plants. The following describes an encapsulated linear ringcusp fusion reactor for providing these and other desired benefitsassociated with compact fusion reactors.

FIG. 1 illustrates applications of a fusion reactor 110, according tocertain embodiments. As one example, one or more embodiments of fusionreactor 110 are utilized by aircraft 101 to supply heat to one or moreengines (e.g., turbines) of aircraft 101. A specific example ofutilizing one or more fusion reactors 110 in an aircraft is discussed inmore detail below in reference to FIG. 2. In another example, one ormore embodiments of fusion reactor 110 are utilized by ship 102 tosupply electricity and propulsion power. While an aircraft carrier isillustrated for ship 102 in FIG. 1, any type of ship (e.g., a cargoship, a cruise ship, etc.) may utilize one or more embodiments of fusionreactor 110. As another example, one or more embodiments of fusionreactor 110 may be mounted to a flat-bed truck 103 in order to providedecentralized power or for supplying power to remote areas in need ofelectricity. As another example, one or more embodiments of fusionreactor 110 may be utilized by an electrical power plant 104 in order toprovide electricity to a power grid. While specific applications forfusion reactor 110 are illustrated in FIG. 1, the disclosure is notlimited to the illustrated applications. For example, fusion reactor 110may be utilized in other applications such as trains, desalinationplants, spacecraft, submarines, and the like.

In general, fusion reactor 110 is a device that generates power byconfining and controlling plasma that is used in a nuclear fusionprocess. Fusion reactor 110 generates a large amount of heat from thenuclear fusion process that may be converted into various forms ofpower. For example, the heat generated by fusion reactor 110 may beutilized to produce steam for driving a turbine and an electricalgenerator, thereby producing electricity. As another example, asdiscussed further below in reference to FIG. 2, the heat generated byfusion reactor 110 may be utilized directly by a turbine of a turbofanor fanjet engine of an aircraft instead of a combustor.

Fusion reactor 110 may be scaled to have any desired output for anydesired application. For example, one embodiment of fusion reactor 110may be approximately 10 m×7 m and may have a gross heat output ofapproximately 100 MW. In other embodiments, fusion reactor 110 may belarger or smaller depending on the application and may have a greater orsmaller heat output. For example, fusion reactor 110 may be scaled insize in order to have a gross heat output of over 200 MW.

FIG. 2 illustrates an example aircraft system 200 that utilizes one ormore fusion reactors 110, according to certain embodiments. Aircraftsystem 200 includes one or more fusion reactors 110, a fuel processor210, one or more auxiliary power units (APUs) 220, and one or moreturbofans 230. Fusion reactors 110 supply hot coolant 240 to turbofans230 (e.g., either directly or via fuel processor 210) using one or moreheat transfer lines. In some embodiments, hot coolant 240 is FLiBe(i.e., a mixture of lithium fluoride (LiF) and beryllium fluoride(BeF₂)) or LiPb. In some embodiments, hot coolant 240 is additionallysupplied to APUs 220. Once used by turbofans 240, return coolant 250 isfed back to fusion reactors 110 to be heated and used again. In someembodiments, return coolant 250 is fed directly to fusion reactors 110.In some embodiments, return coolant 250 may additionally be supplied tofusion reactors 110 from APUs 220.

In general, aircraft system 200 utilizes one or more fusion reactors 110in order to provide heat via hot coolant 240 to turbofans 230.Typically, a turbofan utilizes a combustor that burns jet fuel in orderto heat intake air, thereby producing thrust. In aircraft system 200,however, the combustors of turbofans 230 have been replaced by heatexchangers that utilize hot coolant 240 provided by one or more fusionreactors 110 in order to heat the intake air. This may provide numerousadvantages over typical turbofans. For example, by allowing turbofans230 to operate without combustors that burn jet fuel, the range ofaircraft 101 may be greatly extended. In addition, by greatly reducingor eliminating the need for jet fuel, the operating cost of aircraft 101may be significantly reduced.

FIGS. 3A and 3B illustrate a fusion reactor 110 that may be utilized inthe example applications of FIG. 1, according to certain embodiments. Ingeneral, fusion reactor 110 is an encapsulated linear ring cusp fusionreactor in which encapsulating magnetic coils 150 are used to preventplasma that is generated using internal cusp magnetic coils fromexpanding. In some embodiments, fusion reactor 110 includes an enclosure120 with a center line 115 running down the center of enclosure 120 asshown. In some embodiments, enclosure 120 includes a vacuum chamber andhas a cross-section as discussed below in reference to FIG. 7. Fusionreactor 100 includes internal coils 140 (e.g., internal coils 140 a and140, also known as “cusp” coils), encapsulating coils 150, and mirrorcoils 160 (e.g., mirror coils 160 a and 160 b). Internal coils 140 aresuspended within enclosure 120 by any appropriate means and are centeredon center line 115. Encapsulating coils 150 are also centered on centerline 115 and may be either internal or external to enclosure 120. Forexample, encapsulating coils 150 may be suspended within enclosure 120in some embodiments. In other embodiments, encapsulating coils 150 maybe external to enclosure 120 as illustrated in FIGS. 3A and 3B.

In general, fusion reactor 100 provides power by controlling andconfining plasma 310 within enclosure 120 for a nuclear fusion process.Internal coils 140, encapsulating coils 150, and mirror coils 160 areenergized to form magnetic fields which confine plasma 310 into a shapesuch as the shape shown in FIGS. 3B and 5. Certain gases, such asdeuterium and tritium gases, may then be reacted to make energeticparticles which heat plasma 310 and the walls of enclosure 120. Thegenerated heat may then be used, for example, to power vehicles. Forexample, a liquid metal coolant such as FLiBe or LiPb may carry heatfrom the walls of fusion reactor 110 out to engines of an aircraft. Insome embodiments, combustors in gas turbine engines may be replaced withheat exchangers that utilize the generated heat from fusion reactor 110.In some embodiments, electrical power may also be extracted from fusionreactor 110 via magnetohydrodynamic (MHD) processes.

Fusion reactor 110 is an encapsulated linear ring cusp fusion device.The main plasma confinement is accomplished in some embodiments by acentral linear ring cusp (e.g., center coil 130) with two spindle cuspslocated axially on either side (e.g., internal coils 140). Theseconfinement regions are then encapsulated (e.g., with encapsulatingcoils 150) within a coaxial mirror field provided by mirror coils 160.

The magnetic fields of fusion reactor 110 are provided by coaxiallylocated magnetic field coils of varying sizes and currents. The ringcusp losses of the central region are mitigated by recirculation intothe spindle cusps. This recirculating flow is made stable and compact bythe encapsulating fields provided by encapsulating coils 150. Theoutward diffusion losses and axial losses from the main confinementzones are mitigated by the strong mirror fields of the encapsulatingfield provided by encapsulating coils 150. To function as a fusionenergy producing device, heat is added to the confined plasma 310,causing it to undergo fusion reactions and produce heat. This heat canthen be harvested to produce useful heat, work, and/or electrical power.

Fusion reactor 110 is an improvement over existing systems in partbecause global MHD stability can be preserved and the losses throughsuccessive confinement zones are more isolated due to the scattering ofparticles moving along the null lines. This feature means that particlesmoving along the center line are not likely to pass immediately out ofthe system, but will take many scattering events to leave the system.This increases their lifetime in the device, increasing the ability ofthe reactor to produce useful fusion power.

Fusion reactor 110 has novel magnetic field configurations that exhibitglobal MHD stability, has a minimum of particle losses via open fieldlines, uses all of the available magnetic field energy, and has agreatly simplified engineering design. The efficient use of magneticfields means the disclosed embodiments may be an order of magnitudesmaller than typical systems, which greatly reduces capital costs forpower plants. In addition, the reduced costs allow the concept to bedeveloped faster as each design cycle may be completed much quicker thantypical system. In general, the disclosed embodiments have a simpler,more stable design with far less physics risk than existing systems.

Enclosure 120 is any appropriate chamber or device for containing afusion reaction. In some embodiments, enclosure 120 is a vacuum chamberthat is generally cylindrical in shape. In other embodiments, enclosure120 may be a shape other than cylindrical. In some embodiments,enclosure 120 has a centerline 115 running down a center axis ofenclosure 120 as illustrated. In some embodiments, enclosure 120 has afirst end 320 and a second end 330 that is opposite from first end 320.In some embodiments, enclosure 120 has a midpoint 340 that issubstantially equidistant between first end 320 and second end 330. Across-section of a particular embodiment of enclosure 120 is discussedbelow in reference to FIG. 8.

Some embodiments of fusion reactor 110 may include a center coil 130.Center coil 130 is generally located proximate to midpoint 340 ofenclosure 120. In some embodiments, center coil 130 is centered oncenter line 115 and is coaxial with internal coils 140. Center coil 130may be either internal or external to enclosure 120, may be located atany appropriate axial position with respect to midpoint 340, may haveany appropriate radius, may carry any appropriate current, and may haveany appropriate ampturns.

Internal coils 140 are any appropriate magnetic coils that are suspendedor otherwise positioned within enclosure 120. In some embodiments,internal coils 140 are superconducting magnetic coils. In someembodiments, internal coils 140 are toroidal in shape as shown in FIG.3B. In some embodiments, internal coils 140 are centered on centerline115. In some embodiments, internal coils 140 include two coils: a firstinternal coil 140 a that is located between midpoint 340 and first end320 of enclosure 120, and a second internal coil 140 b that is locatedbetween midpoint 340 and second end 330 of enclosure 120. Internal coils140 may be located at any appropriate axial position with respect tomidpoint 340, may have any appropriate radius, may carry any appropriatecurrent, and may have any appropriate ampturns. A particular embodimentof an internal coil 140 is discussed in more detail below in referenceto FIG. 7.

Encapsulating coils 150 are any appropriate magnetic coils and generallyhave larger diameters than internal coils 140. In some embodiments,encapsulating coils 150 are centered on centerline 115 and are coaxialwith internal coils 140. In general, encapsulating coils 150 encapsulateinternal coils 140 and operate to close the original magnetic lines ofinternal coils 140 inside a magnetosphere. Closing these lines mayreduce the extent of open field lines and reduce losses viarecirculation. Encapsulating coils 150 also preserve the MHD stabilityof fusion reactor 110 by maintaining a magnetic wall that preventsplasma 310 from expanding. Encapsulating coils 150 have any appropriatecross-section, such as square or round. In some embodiments,encapsulating coils 150 are suspended within enclosure 120. In otherembodiments, encapsulating coils 150 may be external to enclosure 120 asillustrated in FIGS. 3A and 3B. Encapsulating coils 150 may be locatedat any appropriate axial position with respect to midpoint 340, may haveany appropriate radius, may carry any appropriate current, and may haveany appropriate ampturns.

Fusion reactor 110 may include any number and arrangement ofencapsulating coils 150. In some embodiments, encapsulating coils 150include at least one encapsulating coil 150 positioned on each side ofmidpoint 340 of enclosure 120. For example, fusion reactor 110 mayinclude two encapsulating coils 150: a first encapsulating coil 150located between midpoint 340 and first end 320 of enclosure 120, and asecond encapsulating coil 150 located between midpoint 340 and secondend 330 of enclosure 120. In some embodiments, fusion reactor 110includes a total of two, four, six, eight, or any other even number ofencapsulating coils 150. In certain embodiments, fusion reactor 110includes a first set of two encapsulating coils 150 located betweeninternal coil 140 a and first end 320 of enclosure 120, and a second setof two encapsulating coils 150 located between internal coil 140 b andsecond end 330 of enclosure 120. While particular numbers andarrangements of encapsulating coils 150 have been disclosed, anyappropriate number and arrangement of encapsulating coils 150 may beutilized by fusion reactor 110.

Mirror coils 160 are magnetic coils that are generally located close tothe ends of enclosure 120 (i.e., first end 320 and second end 330). Insome embodiments, mirror coils 160 are centered on center line 115 andare coaxial with internal coils 140. In general, mirror coils 160 serveto decrease the axial cusp losses and make all the recirculating fieldlines satisfy an average minimum-p, a condition that is not satisfied byother existing recirculating schemes. In some embodiments, mirror coils160 include two mirror coils 160: a first mirror coil 160 a locatedproximate to first end 320 of enclosure 120, and a second mirror coil160 b located proximate to second end 330 of enclosure 120. Mirror coils160 may be either internal or external to enclosure 120, may be locatedat any appropriate axial position with respect to midpoint 340, may haveany appropriate radius, may carry any appropriate current, and may haveany appropriate ampturns.

In some embodiments, coils 130, 140, 150, and 160 are designed or chosenaccording to certain constraints. For example, coils 130, 140, 150, and160 may be designed according to constraints including: high requiredcurrents (maximum in some embodiments of approx. 10 MegaAmp-turns);steady-state continuous operation; vacuum design (protected from plasmaimpingement), toroidal shape, limit outgassing; materials compatiblewith 150C bakeout; thermal build-up; and cooling between shots.

Fusion reactor 110 may include one or more heat injectors 170. Heatinjectors 170 are generally operable to allow any appropriate heat to beadded to fusion reactor 110 in order to heat plasma 310. In someembodiments, for example, heat injectors 170 may be utilized to addneutral beams in order to heat plasma 310 within fusion reactor 110.

In operation, fusion reactor 110 generates fusion power by controllingthe shape of plasma 310 for a nuclear fusion process using at leastinternal coils 140, encapsulating coils 150, and mirror coils 160.Internal coils 140 and encapsulating coils 150 are energized to formmagnetic fields which confine plasma 310 into a shape such as the shapeshown in FIGS. 3B and 5. Gases such as deuterium and tritium may then bereacted to make energetic particles which heat plasma 310 and the wallsof enclosure 120. The generated heat may then be used for power. Forexample, a liquid metal coolant may carry heat from the walls of thereactor out to engines of an aircraft. In some embodiments, electricalpower may also be extracted from fusion reactor 110 via MHD.

In order to expand the volume of plasma 310 and create a more favorableminimum-β geometry, the number of internal coils can be increased tomake a cusp. In some embodiments of fusion reactor 110, the sum ofinternal coils 140, center coil 130, and mirror coils 160 is an oddnumber in order to obtain the encapsulation by the outer ‘solenoid’field (i.e., the magnetic field provided by encapsulating coils 150).This avoids making a ring cusp field and therefor ruining theencapsulating separatrix. Two internal coils 140 and center coil 130with alternating polarizations give a magnetic well with minimum-βcharacteristics within the cusp and a quasi-spherical core plasmavolume. The addition of two axial ‘mirror’ coils (i.e., mirror coils160) serves to decrease the axial cusp losses and more importantly makesthe recirculating field lines satisfy average minimum-β, a condition notsatisfied by other existing recirculating schemes. In some embodiments,additional pairs of internal coils 140 could be added to create moreplasma volume in the well. However, such additions may increase the costand complexity of fusion reactor 110 and may require additional supportsfor coils internal to plasma 310.

In the illustrated embodiments of fusion reactor 110, only internalcoils 140 are within plasma 310. In some embodiments, internal coils 140are suspending within enclosure 120 by one or more supports, such assupport 750 illustrated in FIG. 7. While the supports sit outside thecentral core plasma well, they may still experience high plasma fluxes.Alternatively, internal coils 140 of some embodiments may be amenable tolevitation, which would remove the risk and complexity of having supportstructures within plasma 310.

FIG. 4 illustrates a simplified view of the coils of fusion reactor 110and example systems for energizing the coils. In this embodiment, thefield geometry is sized to be the minimum size necessary to achieveadequate ion magnetization with fields that can be produced by simplemagnet technology. Adequate ion magnetization was considered to be ˜5ion gyro radii at design average ion energy with respect to the width ofthe recirculation zone. At the design energy of 100 eV plasmatemperature there are 13 ion diffusion jumps and at full 20 KeV plasmaenergy there are 6.5 ion jumps. This is the lowest to maintain areasonable magnetic field of 2.2 T in the cusps and keep a modest devicesize.

As illustrated in FIG. 4, certain embodiments of fusion reactor 110include two mirror coils 160: a first mirror coil 160 a locatedproximate to first end 320 of the enclosure and a second magnetic coil160 b located proximate to second end 330 of enclosure 120. Certainembodiments of fusion reactor 110 also include a center coil 130 that islocated proximate to midpoint 340 of enclosure 120. Certain embodimentsof fusion reactor 110 also include two internal coils 140: a firstinternal coil 140 a located between center coil 130 and first end 320 ofenclosure 120, and a second internal coil 140 b located between centercoil 130 and second end 330 of enclosure 120. In addition, certainembodiments of fusion reactor 110 may include two or more encapsulatingcoils 150. For example, fusion reactor 110 may include a first set oftwo encapsulating coils 150 located between first internal coil 140 aand first end 320 of enclosure 120, and a second set of twoencapsulating coils 150 located between second internal coil 140 b andsecond end 330 of enclosure 120. In some embodiments, fusion reactor 110may include any even number of encapsulating coils 150. In someembodiments, encapsulating coils 150 may be located at any appropriateposition along center line 115 other than what is illustrated in FIG. 4.In general, encapsulating coils 150, as well as internal coils 140 andmirror coils 160, may be located at any appropriate position alongcenter line 115 in order to maintain magnetic fields in the correctshape to achieve the desired shape of plasma 310.

In some embodiments, electrical currents are supplied to coils 130, 140,150, and 160 as illustrated in FIG. 4. In this figure, each coil hasbeen split along center line 115 and is represented by a rectangle witheither an “X” or an “O” at each end. An “X” represents electricalcurrent that is flowing into the plane of the paper, and an “O”represents electrical current that is flowing out the plane of thepaper. Using this nomenclature, FIG. 4 illustrates how in thisembodiment of fusion reactor 110, electrical currents flow in the samedirection through encapsulating coils 150, center coil 130, and mirrorcoils 160 (i.e., into the plane of the paper at the top of the coils),but flow in the opposite direction through internal coils 140 (i.e.,into the plane of the paper at the bottom of the coils).

In some embodiments, the field geometry of fusion reactor 110 may besensitive to the relative currents in the coils, but the problem can beadequately decoupled to allow for control. First, the currents toopposing pairs of coils can be driven in series to guarantee that noasymmetries exist in the axial direction. The field in some embodimentsis most sensitive to the center three coils (e.g., internal coils 140and center coil 130). With the currents of internal coil 140 fixed, thecurrent in center coil 130 can be adjusted to tweak the shape of thecentral magnetic well. This region can be altered into an axial-oriented‘bar-bell’ shape by increasing the current on center coil 130 as theincrease in flux ‘squeezes’ the sphere into the axial shape.Alternatively, the current on center coil 130 can be reduced, resultingin a ring-shaped magnetic well at midpoint 340. The radius of centercoil 130 also sets how close the ring cusp null-line comes to internalcoils 140 and may be chosen in order to have this null line close to themiddle of the gap between center coil 130 and internal coils 140 toimprove confinement.

The radius of internal coils 140 serves to set the balance of therelative field strength between the point cusps and the ring cusps forthe central well. The baseline sizes may be chosen such that these fieldvalues are roughly equal. While it would be favorable to reduce the ringcusp losses by increasing the relative flux in this area, a balancedapproach may be more desirable.

In some embodiments, the magnetic field is not as sensitive to mirrorcoils 160 and encapsulating coils 150, but their dimensions should bechosen to achieve the desired shape of plasma 310. In some embodiments,mirror coils 160 may be chosen to be as strong as possible withoutrequiring more complex magnets, and the radius of mirror coils 160 maybe chosen to maintain good diagnostic access to the device center. Someembodiments may benefit from shrinking mirror coils 160, therebyachieving higher mirror ratios for less current but at the price ofreduced axial diagnostic access.

In general, encapsulating coils 150 have weaker magnetic fields than theother coils within fusion reactor 110. Thus, the positioning ofencapsulating coils 150 is less critical than the other coils. In someembodiments, the positions of encapsulating coils 150 are defined suchthat un-interrupted access to the device core is maintained fordiagnostics. In some embodiments, an even number of encapsulating coils150 may be chosen to accommodate supports for internal coils 140. Thediameters of encapsulating coils 150 are generally greater than those ofinternal coils 140, and may be all equal for ease of manufacture andcommon mounting on or in a cylindrical enclosure 120. In someembodiments, encapsulating coils 150 may be moved inward to the plasmaboundary, but this may impact manufacturability and heat transfercharacteristics of fusion reactor 110.

In some embodiments, fusion reactor 110 includes various systems forenergizing center coil 130, internal coils 140, encapsulating coils 150,and mirror coils 160. For example, a center coil system 410, anencapsulating coil system 420, a mirror coil system 430, and an internalcoil system 440 may be utilized in some embodiments. Coil systems410-440 and coils 130-160 may be coupled as illustrated in FIG. 4. Coilsystems 410-440 may be any appropriate systems for driving anyappropriate amount of electrical currents through coils 130-160. Centercoil system 410 may be utilized to drive center coil 130, encapsulatingcoil system 420 may be utilized to drive encapsulating coils 150, mirrorcoil system 430 may be utilized to drive mirror coils 160, and internalcoil system 440 may be utilized to drive internal coils 140. In otherembodiments, more or fewer coil systems may be utilized than thoseillustrated in FIG. 4. In general, coil systems 410-440 may include anyappropriate power sources such as battery banks.

FIG. 5 illustrates plasma 310 within enclosure 120 that is shaped andconfined by center coil 130, internal coils 140, encapsulating coils150, and mirror coils 160. As illustrated, an external mirror field isprovided by mirror coils 160. The ring cusp flow is contained inside themirror. A trapped magnetized sheath 510 that is provided byencapsulating coils 150 prevents detachment of plasma 310. Trappedmagnetized sheath 510 is a magnetic wall that causes plasma 310 torecirculate and prevents plasma 310 from expanding outward. Therecirculating flow is thus forced to stay in a stronger magnetic field.This provides complete stability in a compact and efficient cylindricalgeometry. Furthermore, the only losses from plasma exiting fusionreactor 110 are at two small point cusps at the ends of fusion reactor110 along center line 115. This is an improvement over typical designsin which plasma detaches and exits at other locations.

The losses of certain embodiments of fusion reactor 110 are alsoillustrated in FIG. 5. As mentioned above, the only losses from plasmaexiting fusion reactor 110 are at two small point cusps at the ends offusion reactor 110 along center line 115. Other losses may includediffusion losses due to internal coils 140 and axial cusp losses. Inaddition, in embodiments in which internal coils 140 are suspendedwithin enclosure 120 with one or more supports (e.g., “stalks”), fusionreactor 110 may include ring cusp losses due to the supports.

In some embodiments, internal coils 140 may be designed in such a way asto reduce diffusion losses. For example, certain embodiments of fusionreactor 110 may include internal coils 140 that are configured toconform to the shape of the magnetic field. This may allow plasma 310,which follows the magnetic field lines, to avoid touching internal coils140, thereby reducing or eliminating losses. An example embodiment ofinternal coils 140 illustrating a conformal shape is discussed below inreference to FIG. 7.

FIG. 6 illustrates a magnetic field of certain embodiments of fusionreactor 110. In general, fusion reactor 110 is designed to have acentral magnetic well that is desired for high beta operation and toachieve higher plasma densities. As illustrated in FIG. 6, the magneticfield may include three magnetic wells. The central magnetic well canexpand with high Beta, and fusion occurs in all three magnetic wells.Another desired feature is the suppression of ring cusp losses. Asillustrated in FIG. 6, the ring cusps connect to each other andrecirculate. In addition, good MHD stability is desired in all regions.As illustrated in FIG. 6, only two field penetrations are needed and MHDinterchange is satisfied everywhere.

In some embodiments, the magnetic fields can be altered without anyrelocation of the coils by reducing the currents, creating for exampleweaker cusps and changing the balance between the ring and point cusps.The polarity of the currents could also be reversed to make amirror-type field and even an encapsulated mirror. In addition, thephysical locations of the coils could be altered.

FIG. 7 illustrates an example embodiment of an internal coil 140 offusion reactor 110. In this embodiment, internal coil 140 includes coilwindings 710, inner shield 720, layer 730, and outer shield 740. In someembodiments, internal coil 140 may be suspending within enclosure 120with one or more supports 750. Coil windings 710 may have a width 715and may be covered in whole or in part by inner shield 720. Inner shield720 may have a thickness 725 and may be covered in whole or in part bylayer 730. Layer 730 may have a thickness 735 and may be covered inwhole or in part by outer shield 740. Outer shield may have a thickness745 and may have a shape that is conformal to the magnetic field withinenclosure 120. In some embodiments, internal coil 140 may have anoverall diameter of approximately 1.04 m.

Coil windings 710 form a superconducting coil and carry an electriccurrent that is typically in an opposite direction from encapsulatingcoils 150, center coil 130, and mirror coils 160. In some embodiments,width 715 of coils winding is approximately 20 cm. Coil windings 710 maybe surrounded by inner shield 720. Inner shield 720 provides structuralsupport, reduces residual neutron flux, and shields against gamma raysdue to impurities. Inner shield 720 may be made of Tungsten or any othermaterial that is capable of stopping neutrons and gamma rays. In someembodiments, thickness 725 of inner shield 720 is approximately 11.5 cm.

In some embodiments, inner shield 720 is surrounded by layer 730. Layer730 may be made of lithium (e.g., lithium-6) and may have thickness 735of approximately 5 mm. Layer 730 may be surrounded by outer shield 740.Outer shield 740 may be made of FLiBe and may have thickness 745 ofapproximately 30 cm. In some embodiments, outer shield may be conformalto magnetic fields within enclosure 120 in order to reduce losses. Forexample, outer shield 740 may form a toroid.

FIG. 8 illustrates a cut-away view of enclosure 120 of certainembodiments of fusion reactor 110. In some embodiments, enclosure 120includes one or more inner blanket portions 810, an outer blanket 820,and one or more layers 730 described above. In the illustratedembodiment, enclosure 120 includes three inner blanket portions 810 thatare separated by three layers 730. Other embodiments may have any numberor configuration of inner blanket portions 810, layers 730, and outerblanket 820. In some embodiments, enclosure 120 may have a totalthickness 125 of approximately 80 cm in many locations. In otherembodiments, enclosure 120 may have a total thickness 125 ofapproximately 1.50 m in many locations. However, thickness 125 may varyover the length of enclosure 120 depending on the shape of the magneticfield within enclosure 120 (i.e., the internal shape of enclosure 120may conform to the magnetic field as illustrated in FIG. 3b and thusmany not be a uniform thickness 125).

In some embodiments, inner blanket portions 810 have a combinedthickness 815 of approximately 70 cm. In other embodiments, innerblanket portions 810 have a combined thickness 815 of approximately 126cm. In some embodiments, inner blanket portions are made of materialssuch as Be, FLiBe, and the like.

Outer blanket 820 is any low activation material that does not tend tobecome radioactive under irradiation. For example, outer blanket 820 maybe iron or steel. In some embodiments, outer blanket 820 may have athickness 825 of approximately 10 cm.

FIG. 9 illustrates an example computer system 900. In particularembodiments, one or more computer systems 900 are utilized by fusionreactor 110 for any aspects requiring computerized control. Particularembodiments include one or more portions of one or more computer systems900. Herein, reference to a computer system may encompass a computingdevice, and vice versa, where appropriate. Moreover, reference to acomputer system may encompass one or more computer systems, whereappropriate.

This disclosure contemplates any suitable number of computer systems900. This disclosure contemplates computer system 900 taking anysuitable physical form. As example and not by way of limitation,computer system 900 may be an embedded computer system, a system-on-chip(SOC), a single-board computer system (SBC) (such as, for example, acomputer-on-module (COM) or system-on-module (SOM)), a desktop computersystem, a laptop or notebook computer system, an interactive kiosk, amainframe, a mesh of computer systems, a mobile telephone, a personaldigital assistant (PDA), a server, a tablet computer system, or acombination of two or more of these. Where appropriate, computer system900 may include one or more computer systems 900; be unitary ordistributed; span multiple locations; span multiple machines; spanmultiple data centers; or reside in a cloud, which may include one ormore cloud components in one or more networks. Where appropriate, one ormore computer systems 900 may perform without substantial spatial ortemporal limitation one or more steps of one or more methods describedor illustrated herein. As an example and not by way of limitation, oneor more computer systems 900 may perform in real time or in batch modeone or more steps of one or more methods described or illustratedherein. One or more computer systems 900 may perform at different timesor at different locations one or more steps of one or more methodsdescribed or illustrated herein, where appropriate.

In particular embodiments, computer system 900 includes a processor 902,memory 904, storage 906, an input/output (I/O) interface 908, acommunication interface 910, and a bus 912. Although this disclosuredescribes and illustrates a particular computer system having aparticular number of particular components in a particular arrangement,this disclosure contemplates any suitable computer system having anysuitable number of any suitable components in any suitable arrangement.

In particular embodiments, processor 902 includes hardware for executinginstructions, such as those making up a computer program. As an exampleand not by way of limitation, to execute instructions, processor 902 mayretrieve (or fetch) the instructions from an internal register, aninternal cache, memory 904, or storage 906; decode and execute them; andthen write one or more results to an internal register, an internalcache, memory 904, or storage 906. In particular embodiments, processor902 may include one or more internal caches for data, instructions, oraddresses. This disclosure contemplates processor 902 including anysuitable number of any suitable internal caches, where appropriate. Asan example and not by way of limitation, processor 902 may include oneor more instruction caches, one or more data caches, and one or moretranslation lookaside buffers (TLBs). Instructions in the instructioncaches may be copies of instructions in memory 904 or storage 906, andthe instruction caches may speed up retrieval of those instructions byprocessor 902. Data in the data caches may be copies of data in memory904 or storage 906 for instructions executing at processor 902 tooperate on; the results of previous instructions executed at processor902 for access by subsequent instructions executing at processor 902 orfor writing to memory 904 or storage 906; or other suitable data. Thedata caches may speed up read or write operations by processor 902. TheTLBs may speed up virtual-address translation for processor 902. Inparticular embodiments, processor 902 may include one or more internalregisters for data, instructions, or addresses. This disclosurecontemplates processor 902 including any suitable number of any suitableinternal registers, where appropriate. Where appropriate, processor 902may include one or more arithmetic logic units (ALUs); be a multi-coreprocessor; or include one or more processors 902. Although thisdisclosure describes and illustrates a particular processor, thisdisclosure contemplates any suitable processor.

In particular embodiments, memory 904 includes main memory for storinginstructions for processor 902 to execute or data for processor 902 tooperate on. As an example and not by way of limitation, computer system900 may load instructions from storage 906 or another source (such as,for example, another computer system 900) to memory 904. Processor 902may then load the instructions from memory 904 to an internal registeror internal cache. To execute the instructions, processor 902 mayretrieve the instructions from the internal register or internal cacheand decode them. During or after execution of the instructions,processor 902 may write one or more results (which may be intermediateor final results) to the internal register or internal cache. Processor902 may then write one or more of those results to memory 904. Inparticular embodiments, processor 902 executes only instructions in oneor more internal registers or internal caches or in memory 904 (asopposed to storage 906 or elsewhere) and operates only on data in one ormore internal registers or internal caches or in memory 904 (as opposedto storage 906 or elsewhere). One or more memory buses (which may eachinclude an address bus and a data bus) may couple processor 902 tomemory 904. Bus 912 may include one or more memory buses, as describedbelow. In particular embodiments, one or more memory management units(MMUs) reside between processor 902 and memory 904 and facilitateaccesses to memory 904 requested by processor 902. In particularembodiments, memory 904 includes random access memory (RAM). This RAMmay be volatile memory, where appropriate. Where appropriate, this RAMmay be dynamic RAM (DRAM) or static RAM (SRAM). Moreover, whereappropriate, this RAM may be single-ported or multi-ported RAM. Thisdisclosure contemplates any suitable RAM. Memory 904 may include one ormore memories 904, where appropriate. Although this disclosure describesand illustrates particular memory, this disclosure contemplates anysuitable memory.

In particular embodiments, storage 906 includes mass storage for data orinstructions. As an example and not by way of limitation, storage 906may include a hard disk drive (HDD), a floppy disk drive, flash memory,an optical disc, a magneto-optical disc, magnetic tape, or a UniversalSerial Bus (USB) drive or a combination of two or more of these. Storage906 may include removable or non-removable (or fixed) media, whereappropriate. Storage 906 may be internal or external to computer system900, where appropriate. In particular embodiments, storage 906 isnon-volatile, solid-state memory. In particular embodiments, storage 906includes read-only memory (ROM). Where appropriate, this ROM may bemask-programmed ROM, programmable ROM (PROM), erasable PROM (EPROM),electrically erasable PROM (EEPROM), electrically alterable ROM (EAROM),or flash memory or a combination of two or more of these. Thisdisclosure contemplates mass storage 906 taking any suitable physicalform. Storage 906 may include one or more storage control unitsfacilitating communication between processor 902 and storage 906, whereappropriate. Where appropriate, storage 906 may include one or morestorages 906. Although this disclosure describes and illustratesparticular storage, this disclosure contemplates any suitable storage.

In particular embodiments, I/O interface 908 includes hardware,software, or both, providing one or more interfaces for communicationbetween computer system 900 and one or more I/O devices. Computer system900 may include one or more of these I/O devices, where appropriate. Oneor more of these I/O devices may enable communication between a personand computer system 900. As an example and not by way of limitation, anI/O device may include a keyboard, keypad, microphone, monitor, mouse,printer, scanner, speaker, still camera, stylus, tablet, touch screen,trackball, video camera, another suitable I/O device or a combination oftwo or more of these. An I/O device may include one or more sensors.This disclosure contemplates any suitable I/O devices and any suitableI/O interfaces 908 for them. Where appropriate, I/O interface 908 mayinclude one or more device or software drivers enabling processor 902 todrive one or more of these I/O devices. I/O interface 908 may includeone or more I/O interfaces 908, where appropriate. Although thisdisclosure describes and illustrates a particular I/O interface, thisdisclosure contemplates any suitable I/O interface.

In particular embodiments, communication interface 910 includeshardware, software, or both providing one or more interfaces forcommunication (such as, for example, packet-based communication) betweencomputer system 900 and one or more other computer systems 900 or one ormore networks. As an example and not by way of limitation, communicationinterface 910 may include a network interface controller (NIC) ornetwork adapter for communicating with an Ethernet or other wire-basednetwork or a wireless NIC (WNIC) or wireless adapter for communicatingwith a wireless network, such as a WI-FI network. This disclosurecontemplates any suitable network and any suitable communicationinterface 910 for it. As an example and not by way of limitation,computer system 900 may communicate with an ad hoc network, a personalarea network (PAN), a local area network (LAN), a wide area network(WAN), a metropolitan area network (MAN), or one or more portions of theInternet or a combination of two or more of these. One or more portionsof one or more of these networks may be wired or wireless. As anexample, computer system 900 may communicate with a wireless PAN (WPAN)(such as, for example, a BLUETOOTH WPAN), a WI-FI network, a WI-MAXnetwork, a cellular telephone network (such as, for example, a GlobalSystem for Mobile Communications (GSM) network), or other suitablewireless network or a combination of two or more of these. Computersystem 900 may include any suitable communication interface 910 for anyof these networks, where appropriate. Communication interface 910 mayinclude one or more communication interfaces 910, where appropriate.Although this disclosure describes and illustrates a particularcommunication interface, this disclosure contemplates any suitablecommunication interface.

In particular embodiments, bus 912 includes hardware, software, or bothcoupling components of computer system 900 to each other. As an exampleand not by way of limitation, bus 912 may include an AcceleratedGraphics Port (AGP) or other graphics bus, an Enhanced Industry StandardArchitecture (EISA) bus, a front-side bus (FSB), a HYPERTRANSPORT (HT)interconnect, an Industry Standard Architecture (ISA) bus, an INFINIBANDinterconnect, a low-pin-count (LPC) bus, a memory bus, a Micro ChannelArchitecture (MCA) bus, a Peripheral Component Interconnect (PCI) bus, aPCI-Express (PCIe) bus, a serial advanced technology attachment (SATA)bus, a Video Electronics Standards Association local (VLB) bus, oranother suitable bus or a combination of two or more of these. Bus 912may include one or more buses 912, where appropriate. Although thisdisclosure describes and illustrates a particular bus, this disclosurecontemplates any suitable bus or interconnect.

Herein, a computer-readable non-transitory storage medium or media mayinclude one or more semiconductor-based or other integrated circuits(ICs) (such, as for example, field-programmable gate arrays (FPGAs) orapplication-specific ICs (ASICs)), hard disk drives (HDDs), hybrid harddrives (HHDs), optical discs, optical disc drives (ODDs),magneto-optical discs, magneto-optical drives, floppy diskettes, floppydisk drives (FDDs), magnetic tapes, solid-state drives (SSDs),RAM-drives, SECURE DIGITAL cards or drives, any other suitablecomputer-readable non-transitory storage media, or any suitablecombination of two or more of these, where appropriate. Acomputer-readable non-transitory storage medium may be volatile,non-volatile, or a combination of volatile and non-volatile, whereappropriate.

Herein, “or” is inclusive and not exclusive, unless expressly indicatedotherwise or indicated otherwise by context. Therefore, herein, “A or B”means “A, B, or both,” unless expressly indicated otherwise or indicatedotherwise by context. Moreover, “and” is both joint and several, unlessexpressly indicated otherwise or indicated otherwise by context.Therefore, herein, “A and B” means “A and B, jointly or severally,”unless expressly indicated otherwise or indicated otherwise by context.

The scope of this disclosure encompasses all changes, substitutions,variations, alterations, and modifications to the example embodimentsdescribed or illustrated herein that a person having ordinary skill inthe art would comprehend. The scope of this disclosure is not limited tothe example embodiments described or illustrated herein. Moreover,although this disclosure describes and illustrates respectiveembodiments herein as including particular components, elements,functions, operations, or steps, any of these embodiments may includeany combination or permutation of any of the components, elements,functions, operations, or steps described or illustrated anywhere hereinthat a person having ordinary skill in the art would comprehend.Furthermore, reference in the appended claims to an apparatus or systemor a component of an apparatus or system being adapted to, arranged to,capable of, configured to, enabled to, operable to, or operative toperform a particular function encompasses that apparatus, system,component, whether or not it or that particular function is activated,turned on, or unlocked, as long as that apparatus, system, or componentis so adapted, arranged, capable, configured, enabled, operable, oroperative.

What is claimed is:
 1. A system comprising: an enclosure comprising: afirst end and a second end that is opposite from the first end; and amidpoint that is substantially equidistant between the first and secondends of the enclosure; two superconducting internal magnetic coilssuspended within an interior of the enclosure and coaxial with a centeraxis of the enclosure, the two internal magnetic coils each having atoroidal shape, the two internal magnetic coils comprising: a firstinternal magnetic coil located between the midpoint and first end of theenclosure; and a second internal magnetic coil located between themidpoint and the second end of the enclosure; wherein the internal coilseach have a radius configured to balance the relative field strengthbetween a plurality of point cusps and a plurality of ring cusps; aplurality of encapsulating magnetic coils co-axial with a center axis ofthe enclosure, the encapsulating magnetic coils having a larger diameterthan the internal magnetic coils, the plurality of encapsulatingmagnetic coils comprising; at least two first encapsulating magneticcoils located between the midpoint and the first and of the enclosure;and at east two second encapsulating magnetic coils located between themidpoint and the second end of the enclosure; a center magnetic coilco-axial with a center axis of the enclosure and located proximate tothe midpoint of the enclosure; and two mirror magnetic coils co-axialwith a center axis of the enclosure and comprising: a first mirrormagnetic coil located proximate to the first end of the enclosure; asecond mirror magnetic coil located proximate to the second end of theenclosure; one or more coil systems configured to supply the magneticcoils with electrical currents, to form magnetic fields for confiningplasma within a magnetized sheath in the enclosure, wherein themagnetized sheath and plasma confined within the magnetized sheathencircle each of the two internal magnetic coils; wherein the centermagnetic coil is disposed outside the interior of the enclosure.
 2. Thesystem of claim 1, wherein the one or more coil systems comprise: acenter coil system configured to supply first electrical currentsflowing in a first direction through the center magnetic coil; aninternal coil system configured to supply second electrical currentsflowing in a second direction through each of the two internal magneticcoils; an encapsulating coil system configured to supply thirdelectrical currents flowing in the first direction through each of theplurality of encapsulating magnetic coils; and a mirror coil systemconfigured to supply fourth electrical currents flowing in the firstdirection through each of the two mirror magnetic coils.
 3. The systemof claim 1, wherein the enclosure comprises an outer blanket and aninner blanket, the outer blanket comprising steel or iron and the innerblanket comprising beryllium or a mixture of lithium fluoride (LiF) andberyllium fluoride (BeF2)(FLiBe).
 4. The system of claim 1, wherein eachof the two internal magnetic coils comprises: a core comprising aplurality of coil windings; an inner shield surrounding the core; aprotective layer surrounding the inner shield; and an outer shieldsurrounding the protective layer.
 5. A system comprising: an enclosurecomprising: a first end and a second end that is opposite from the firstend; and a midpoint that is substantially equidistant between the firstand second ends of the enclosure; two superconducting internal magneticcoils suspended within an interior of the enclosure, each internalmagnetic coil positioned on an opposite side of the midpoint of theenclosure from the other internal magnetic coil; wherein the internalcoils each have a radius configured to balance the relative fieldstrength between a plurality of point cusps and a plurality of ringcusps; one or more encapsulating magnetic coils positioned on each sideof the midpoint of the enclosure, each encapsulating magnetic coil beingcoaxial with the internal magnetic coils; a center magnetic coilco-axial with the center of the enclosure and located proximate to themidpoint of the enclosure; two mirror magnetic coils coaxial with theinternal magnetic coils, each mirror magnetic coil positioned on anopposite side of the midpoint of the enclosure from the other mirrormagnetic coil; and one or more coil systems configured to supply themagnetic coils with electrical currents, to form magnetic fields forconfining plasma within a magnetized sheath in the enclosure, whereinthe magnetized sheath and plasma confined within the magnetized sheathencircle each of the two internal magnetic coils; wherein the centermagnetic coil is disposed outside the interior of the enclosure.
 6. Thesystem of claim 5, further comprising a center magnetic coil locatedproximate to the midpoint of the enclosure, the center magnetic coilbeing coaxial with the internal magnetic coils.
 7. The system of claim6, wherein: the two internal magnetic coils comprises: a first internalmagnetic coil located between the center magnetic coil and the first endof the enclosure; and a second internal magnetic coil located betweenthe center magnetic coil and the second end of the enclosure; the one ormore encapsulating magnetic coils positioned on each side of themidpoint of the enclosure comprises: a first set of two encapsulatingmagnetic coils located between the first internal magnetic coil and thefirst end of the enclosure; and a second set of two encapsulatingmagnetic coils located between the second internal magnetic coil and thesecond end of the enclosure; and the two mirror magnetic coilscomprises: a first mirror magnetic coil located proximate to the firstend of the enclosure; and a second mirror magnetic coil locatedproximate to the second end of the enclosure.
 8. The system of claim 5,wherein the enclosure comprises an outer blanket and an inner blanket,the outer blanket comprising steel or iron and the inner blanketcomprising beryllium or a mixture of lithium fluoride (LiF) andberyllium fluoride (BeF2)(FLiBe).
 9. The system of claim 5, wherein eachof the two internal magnetic coils comprises: a core comprising aplurality of coil windings; an inner shield surrounding the core; aprotective layer surrounding the inner shield; and an outer shieldsurrounding the protective layer.
 10. The system of claim 5, wherein theone or more coil systems comprise: a center coil system configured tosupply first electrical currents flowing in a first direction throughthe center magnetic coil; an internal coil system configured to supplysecond electrical currents flowing in a second direction through each ofthe two internal magnetic coils; an encapsulating coil system configuredto supply third electrical currents flowing in the first directionthrough each of the plurality of encapsulating magnetic coils; and amirror coil system configured to supply fourth electrical currentsflowing in the first direction through each of the two mirror magneticcoils.
 11. The system of claim 5, wherein the encapsulating magneticcoils are external to the enclosure.